Selective fruit and seed maturation in Asphodelus albus Miller (Liliaceae)

The fruiting patterns of the rhizomatous perennial Asphodelus albus Miller (Liliaceae) were studied in five populations during 1989 and in one population over 3 years (1988–1990). Fruit/flower (Fr/Fl) ratio and seed/ovule (S/O) ratio varied markedly between populations. Although there were differences between years within the population studied over 3 years, these variations, although statistically signifcant, were less important than those between populations. Neither flowering phenology nor plant size influenced Fr/Fl or S/O ratios. Field experiments tested whether fruit and seed set were pollenor resource-limited. Hand-pollination had no effect on Fr/Fl or S/O ratios, but the reduction of resources by defoliation at the time of flowering decreased both relative components of fecundity. Manipulation of resources by hand-thinning flowers and tiny fruits had no demonstrable effect on these ratios, although brood size of individual fruits was significantly affected. It may be concluded that fruit maturation is resource-limited rather than pollen-limited. Most of the fruits aborted early in the fruiting season, and fruits with higher numbers of developing seeds had a lower probability of abortion than fruits with fewer seeds. Analyses of position effects revealed that the fruits in lower positions in the inflorescence matured preferentially. Furthermore, the two ovules in the same carpel tended either both to fail or both to develop into seeds. The plant's ability to selectively mature only high quality embryos may be limited.     

Floral sex allocation and reproductive success within inflorescences of Hosta ventricosa,a pseudogamous apomict

Aims Within inflorescences of sexually reproducing hermaphrodites, the production of ovules, fruits and seeds commonly declines from basal (early-opening) to distal (late-opening) flowers, while pollen production remains constant or only changes slightly, with the result that distal (late-opening) flowers become functionally male. However, few empirical studies have specifically examined whether or not changes in allocation to pollen production actually lead to changes in the number of seeds sired, a more direct measure of male fitness. In pseudogamous apomicts, fitness depends on the number of seeds produced; thus, a contrasting pattern of variation in the pollen-to-ovule (P/O) ratio within inflorescences might be expected.Methods We investigated floral sex allocation and reproductive success within racemes of Hosta ventricosa, a pseudogamous apomictic hermaphrodite possessing flowers that open acropetally. We quantified variations in pollen number, ovule number, the P/O ratio and fruit and seed production, from 2007 to 2011, among flowers within racemes of four populations of H. ventricosa in southwest China. Ecological causes for fruit and seed production were evaluated by observing patterns of pollen deposition, flower removal and supplemental pollination.Important findings Pollen number, ovule number and the P/O ratio declined from basal-to-distal positions in all sampled populations (years). Fruit and seed production decreased distally in most populations (years). Low fruit and seed set of distal flowers was not due to pollen limitation because pollen deposition never declined distally and the low fruit and seed set of distal flowers remained even after supplementary pollination was provided. The flower-removal experiment indicated that inter-fruit competition for resources among flowers was common. The low P/O ratio of distal flowers in H. ventricosa might be favored because they were unable to obtain fitness by donating pollen and siring seeds on other plants. Our study may help to understand the adaptive significance of sex allocation among flowers within inflorescences of sexually reproducing hermaphrodites.     

Variation of pollen limitation in the early flowering Mediterranean geophyte Narcissus assoanus (Amaryllidaceae)

A recent literature review indicates that pollen limitation of female fertility is a common feature of flowering plants. Despite the ecological and evolutionary significance of pollen limitation, most studies have only examined fertility in a single population at one time. Here we investigate pollen limitation of fruit and seed set in five populations of Narcissus assoanus, a self- sterile, insect-pollinated geophyte, over 2–3 years in southern France. In common with many early spring flowering plants, pollinator visitation to N. assoanus is often infrequent. Supplemental hand-pollination of flowers with outcross pollen significantly increased overall fruit and seed set by 11% and 19%, respectively. Four of the five populations experienced some pollen limitation during the study. For a given year, there was significant variation in pollen limitation among populations. Two of the populations were pollen limited in one year but not in other years in which they were studied. Seed:ovule ratios for open- and hand-pollinated flowers averaged 0.29 and 0.33, respectively. While hand pollination significantly increased the seed:ovule ratio, the low value obtained indicates that the majority of ovules in flowers do not mature seeds despite hand pollination. The role of genetic and environmental factors governing low seed:ovule ratios in N. assoanus is discussed. Received: 28 December 1999 / Accepted: 6 April 2000     

Effect of ovule position within the pod on the probability of seed production in Bauhinia ungulata (Fabaceae)

BACKGROUND AND AIMS: It has been claimed that ovules linearly ordered within a fruit differ in their probabilities of reaching maturity. This was investigated by studying the effect the position of an ovule within the pod has on seed abortion and seed production in Bauhinia ungulata. METHODS: Fruits collected during the dry seasons of 1999, 2000 and 2001 were opened, and the number, position and status of each ovule within the fruit were recorded. A GLM model was used to assess the effects of population, tree identity and ovule position within the pod on ovule fertilization, seed abortion, seed damage and seed maturation in two populations of B. ungulata. KEY RESULTS: Nearly 30% of the ovules were not fertilized in 1999; this percentage dropped to 5% the following two years. Seed abortion (50%) and seed damage (15%) were the same every year during the study period. Only 15% of the initial ovules developed into mature seeds in 1999; this value increased to 35% in 2000 and 2001. However, seed survivorship was dependent on the position of the ovule within the pod; non-fertilized and early aborted ovules were found more often near the basal end of the ovary. The frequency of seed damage was not affected by position. Mature seeds were found mainly in the stylar half of fruits, where ovules are likely to be fertilized by fast pollen tubes. CONCLUSIONS: The pattern of seed production in B. ungulata is non-random but is dependent upon the position of the ovule within the pod. The results suggest that the seeds produced within a fruit might differ in their vigour.     

Pollination intensity and potential seed set in Passiflora vitifolia

Summary Initial seed set and fruit set were pollen-limited in a Costa Rican population of Passiflora vitifolia, a self-incompatible species with 200–350 ovules per flower. Pollination intensity was measured by counting the number of allogamous pollen grains on stigmas of the large one-day flowers. Hand-pollinations demonstrated that 25–50 pollen grains are required for fruit set, and >450 are needed for maximum seed set, with a pollen:seed ratio of about 1.6:1.0. Hummingbirds (Phaethornis superciliosus) delivered sufficient allogamous pollen for maximum seed set to only 28% of the flowers examined. Naturally pollinated flowers yielded fewer fruits and fewer seeds per fruit than those pollinated by hand. Most pollen transferred by humming-birds was self-incompatible; emasculated flowers yielded higher seed set than flowers with intact anthers. Visitation rates did not provide a good index of effective pollination.There were significant differences in ovule number, maximum seed set, and maximum per cent seed set among individual vines. More than half of an individual's flowers failed to set fruit, whether pollinated by birds or by hand. In this population, maximum reproductive potential may be limited by maternal resources for fruit development, but seed set varies with pollination intensity. Pollen-limited seed set may be a disadvantage of self-incompatibility, especially in species with many-seeded fruits.     

Patterns of fruit and seed production inBauhinia ungulata (Leguminosae)

Patterns of seed and fruit production ofBauhinia ungulata, a small tree legume indigenous in tropical America, were studied in Costa Rica. Only about 8% of flowers produced fruits. The average pod had 19 ovules and about two thirds of these began seed development, with mature pods containing an average of 9.7 mature undamaged seeds. About half of the mature pods were damaged by herbivores and within these, 27% of ovules or seeds had been eaten. Among trees there was no significant variation in pod production, but the number of ovules per pod and seed production per pod varied significantly. Within infructescences most pods were retained at middle positions. Within pods, the probability of an ovule developing into a seed increased toward the distal end. The pattern of seed and fruit production in this species agrees well in general with that reported for other neotropical legumes. The abortion of seeds and fruits can be regarded as a way of controlling maternal investment, and as a response to herbivory.     

The role of endogenous gibberellin in seed and fruit development of tomato: Studies with a gibberellin-deficient mutant

The role of endogenous gibberellin (GA) in seed and fruit development was studied with the use of the GA-deficient ga-1 mutant of tomato ( Lycopersicon esculentum Mill. cv. Moneymaker). Flowers of the ga-1 mutant were abnormal and sterile, but parthenocarpic fruit development was observed occasionally on the dwarf plants. A single application of GA₄₊₇ restored the fertility of the mutant flowers and resulted in seed set. Development of GA-producing and GA-deficient seeds in GA-deficient fruits was compared by pollination of ga-1/ga-1 flowers with wild-type or ga-1 pollen, respectively. In ga-1/ga-1 seed dehydration started about 1 week earlier than in Ga-1/ga-1 seeds. Ultimate fresh and dry weights of mature Ga-1/ga-1 seeds were higher than those of ga-1/ga-1 seeds and showed negative correlations with the total number of seeds per fruit. Total content and composition of seed proteins were not influenced by the GA-deficiency. Germination of the mature seeds depended on embryonal GA synthesis and was not influenced by maternal GA production. Final fresh weight of the ga-1/ga-1 fruits was positively correlated with the number of seeds per fruit. In these fruits, the minimum number of seeds for growth above the parthenocarpic level was about 10 or 35 in the presence of Ga-1/ga-1 or ga-1/ga-1 seeds, respectively. Fruits containing GA-producing seeds reached a higher fresh weight than those containing GA-deficient seeds, and their ripening was delayed by one week. It is concluded that gibberellin is indispensable for the development of fertile flowers and for seed germination, but only promoting in later stages of fruit and seed development.     

Patterns of seed mass variation and their effects on seedling traits inAlliaria petiolata (Brassicaceae)

Seed mass is considered to be the least plastic component of reproductive yield. Yet, in invasive populations of garlic mustard, Alliaria petiolata, seed mass was highly variable (eightfold among populations, 2.5-7.5 fold within populations, two-threefold within individuals, and 1.4-1.8 fold within fruits). Variation in seed mass among populations explained nearly half of the total variance. Variation among seeds within fruits accounted for a further 25% of variance. Individual seed mass within a plant decreased with increased distance from the main stem, suggesting that access to parental resources limits seed size in a predictable manner. MANOVAs and Roy-Bargmann stepdown analyses revealed significant effects of seed mass, but not seed position (within a fruit or within an infructescence), on an array of subsequent seedling traits. Smaller seeds germinated significantly earlier, and seedlings from small seeds produced their first primary leaves significantly later and grew significantly taller. After accounting for seed mass as a covariate, only one seedling trait, date of first leaf emergence, was affected by seed position in a fruit. Differences in seed mass may therefore affect seedling recruitment via effects on early seedling growth in this weedy species.     

Factors Influencing Seed: Ovule Ratios and Reproductive Success in Four Cleistogamous Species: A Comparison between Two Flower Types

Abstract: Ovule and seed numbers, and the ratio between the two, were determined in chasmogamous (CH) and cleistogamous (CL) flowers/fruits in four perennial herbs: Viola hirta, V. mirabilis, V. riviniana, and Oxalis acetosella. The results were applied to data from earlier studies on fruit set and progeny performance in these species, to find implications for factors influencing seed: ovule (S: O) ratio, to relate S: O ratio to other fitness components, and to compare final numbers of seedlings per initiated ovule between the two reproductive modes. Mechanisms considered to have a potential impact on S: O ratios were pollen limitation, resource limitation, and "genetic load". In V. mirabilis and O. acetosella, mean S: O ratio was significantly higher in the CL phase than in the CH phase; in V. hirta and V. riviniana, there was no difference. Pollen limitation seemed improbable as a factor important for seed set in all species, and no indication was found of resource limitation. There was a negative correlation between S: O ratio and seed germination rate in O. acetosella, indicating that seed abortion, particularly in CH fruits, may be a way to purge inferior zygotes. The high CH S: O ratios in all species suggest that substantial selfing also occurs in this phase. The final number of seedlings per ovule did not differ significantly between modes in any of the species, partly due to poorer germination in CL seeds. This indicates that, despite the often lower pre-emergent reproductive success (fruit and seed set) in the CH phase, total reproductive success will not differ between the two modes because post-emergent selection is stronger on CL progeny. The strongest limitation on pre-emergent reproductive success in both phases is apparently related to flower/fruit abortion.     

Post-floral perianth functionality: contribution of persistent sepals to seed development in Helleborus foetidus (Ranunculaceae)

The perianth persists after flowering in many plants, yet its post-floral functionality has been little investigated, and the few studies available provide ambiguous evidence. This paper tests the hypothesis that the green persistent sepals of the perennial herb, Helleborus foetidus, contribute to the plant's fitness by enhancing seed number and/or size. Post-floral contribution of the calyx to fruit and seed development was evaluated by manipulating sepal number and measuring the effect on follicle size, seed set, seeds per follicle, and mean seed mass. The allometric relationship between calyx size and follicle mass was examined for flower buds, open flowers, and immature fruits differing in follicle number. Calyx manipulation had no significant effect on follicle size, seed set, or number of seeds per follicle, but it did have a significant influence on the size of individual seeds. Calyx size and mean seed mass were positively, linearly related. The calyx mass/seed number ratio declined with increasing number of follicles per fruit. The persistent sepals of Helleborus do contribute resources to the development of seeds, although there is not evidence of post-floral allometric adjustment of the calyx mass/follicle number ratio that could compensate for variations in seed number per fruit.     

Competition and the compensatory regulation of fruit and seed set in the perennial herb Epilobium dodonaei (Onagraceae)

I studied the effects of competition and soil fertilization on variation of seed yield components of the outcrossing perennial Epilobium dodonaei Vill. using a randomized complete block design. Fertilization as a main effect was not significant. Competition, however, reduced the number of flower buds per shoot (-29%), the number of ovules per fruit (-12%), and the number of ripe fruits per shoot (-51%). In addition, competition caused an increase in abortion of flower buds. Consequently the fruit/flower bud ratio decreased from 0.71 to 0.47. Average seed mass was not reduced significantly by competition. Some of the negative effects of competition on fruit production were mitigated by fertilization. However, competition considerably reduced the proportion of late-aborted seeds, which resulted in an increase of the seed/ovule ratio from 0.31 to 0.49 (+58%). As a consequence of this compensation, the reduction in the number of seeds per shoot due to competition was not significant. At the level of the genet, competition had a strong effect on seed yield due to decreases in the number of shoots produced. I discuss patterns of regulation at consecutive levels of reproduction. Shoots of plants suffering from competition initially invested less in reproductive structures than the control and showed a higher abortion rate of less costly structures early in reproductive development, but also had a lower abortion rate later in their development. The observed compensatory pattern in yield components illustrates the fine-tuning regulation capacity at different levels of reproductive development in plants.     

Single-Seeded Fruits and Seedling Establishment in Dalbergia miscolobium Benth. (Papilionaceae)1

Dalbergia miscolobium (Papilionaceae) is a tree of the Brazilian cerrado that produces ovaries with two ovules. Only one ovule usually matures, but when two mature, they are smaller than seeds of single-seeded pods. Germination percentage was lower in small seeds than in medium or large seeds. In general, small seeds gave rise to smaller seedlings (dry mass) than did medium and large seeds. The root/shoot ratio, however, was very similar for the first six months, indicating that this ratio is consistent across seedling sizes. There was no correlation between seed size and relative growth rate. Single-seeded fruit production in D. miscolobium resulted in greater seed reserves and increased fruit dispersal distance; single-seeded fruits were lighter than double-seeded ones. Together, these two features should increase the probability of successful seedling establishment of seeds from single-seeded versus double-seeded fruits.     

药物植物桃儿七不同种群种子产量初步研究

对药用植物桃儿七5个不同种群种子产量的研究表明：各种群中每花平均胚珠数、每果实平均种子数及种群平均结实率与种群所在的海拔高度呈正相关;不同种群个体平均胚珠数的变异范围为58.97-87.97,平均种子数变异范围为40.02-80.58,平均结籽率变异范围为61.29%-91.60%;果料内单粒种子平均干重与种群分布海拔呈明显负相关,与果实内种子数呈弱负相关;同一种群在不同年份间平均各上子产量差异不大;种子产量除主要受个体营养状况影响外,还受海拔及其它因素的影响;果实内种子数与果实大小及重量呈正相关,但单粒种子平均重量与果实大小及果实内种子总重量无显著相关。     

Selective seed abortion affects the performance of the offspring in Bauhinia ungulata

BACKGROUND AND AIMS: Under the microgametophytic competition hypothesis, a non-random pattern of seed abortion is expected, in which only the most vigorous seeds reach maturity. In a previous study, it was found that Bauhinia ungulata (Fabaceae) exhibits a pattern of seed abortion dependent on the position of the ovule within the ovary; ovules located in the stylar half of the fruit, close to the point of entry of pollen tubes to the ovary, have a low probability of seed abortion, whereas ovules in the basal half of the fruit are aborted with a high probability. METHODS: A series of experimental fruits was generated, in which ovules from either the stylar (treatments 1 and 2) or the basal (treatments 3 and 4) half of fruits were destroyed, to evaluate whether these patterns of selective seed abortion have an effect on the vigour of the offspring in B. ungulata. KEY RESULTS: Only 53 % of the seed from control fruits germinated. Seed set in fruits from treatments 1 and 2 showed a significantly lower (33-43 %) percentage of germination; the germination of seeds from fruits in treatments 3 and 4 (49-51 %) did not differ from control seeds. In addition, it was found that the differences in vigour of the offspring are not random with respect to the position of the ovule in the pod. CONCLUSIONS: The overall performance of the seeds correlated with their likelihood of maturation. Seeds located at the basal half of the treatment fruits showed lower values of vigour than seeds located on the stylar half. The differences were more marked for early measures of fitness.     

不同居群准噶尔无叶豆果实和种子特性及种子萌发差异

研究准噶尔无叶豆(Eremosparton songoricum) 6个居群间果实和种子特性及种子萌发差异, 以揭示异质生境下准噶尔无叶豆果实和种子的生态适应机制。结果显示: 居群间准噶尔无叶豆的植株距离(F = 2.34, p = 0.03)和植株冠幅(F = 8.49, p < 0.01)存在显著差异, 沙漠北缘E、F居群和沙漠腹地C居群(受人类干扰剧烈)的植株距离和植株冠幅高于沙漠腹地A、B、D居群; 居群间准噶尔无叶豆果实和种子的长度、宽度、厚度、重量存在显著差异, 居群E、F和C的大部分参数显著高于其他沙漠腹地居群; 居群间果实多子性(F = 6.96, p < 0.01)也存在显著差异, 居群C的果实多子性最高((32.50 ± 4.79)%); 萌发结果表明, 居群间新鲜的成熟种子萌发不存在显著差异, 且萌发率都低于15%; 所有居群的大部分种子都存在物理性休眠现象, 人为划破种皮能显著提高种子萌发率, 但在低温(15/5 ℃)条件下, 所有居群的种子萌发率都较低, 说明低温抑制了种子萌发; 经人为划破种皮解除物理休眠后, 种子的休眠没有完全释放, 居群C、E和F (大种子居群)的种子萌发率显著高于居群A、B和D (小种子居群) (F = 30.77, p < 0.01), 说明准噶尔无叶豆种子不仅存在物理性休眠现象, 也可能存在生理休眠现象。不同程度的种子复合休眠可能是准噶尔无叶豆不同居群适应古尔班通古特沙漠的重要生存策略。     

Floral sex ratios, disease and seed set in dioecious Silene dioica

1 In the dioecious, perennial herb Silene dioica , the density of pollen donors in a population is determined by overall plant density, the sex ratio and the proportion of plants infected with the anther-smut fungus Microbotryum violaceum , which results in permanent sterility of both male and female plants.
2 Pollinators ( Bombus spp.) were found to prefer male flowers and to avoid diseased flowers. This may result in an overall lower visitation frequency and increased risk for pollen limitation in populations with a low density of males or a high incidence of disease.
3 Compared with open-pollinated flowers, hand pollination resulted in a significant increase in the number of seeds produced per fruit in populations with an experimentally reduced proportion of males (25% and 50% male flowers) but not in a naturally male-dominated population (75% male flowers). Seed production per plant was increased by hand pollination only in the most female-dominated population. Because the floral sex ratio is often male-biased, resources rather than pollen availability are likely to set the upper limit for total seed production per individual in most healthy populations of S. dioica.
4 There was a negative relationship between seed set and incidence of disease across 22 populations in both years of a field study. However, there was no consistent difference between the responses of highly diseased populations (incidence 30–56%) and populations with a low disease incidence (incidence 0–8%) to hand pollination.
5 In a greenhouse experiment with cloned hand-pollinated females, the presence of spores on healthy flowers was found to reduce seed set significantly. In highly diseased populations, therefore, the frequent deposition of spores by flower visitors onto remaining healthy plants may decrease seed production below the potential level determined by resources or pollen availability.     

毛翠雀花花序内的性分配和繁殖成功

两性花植物花序内不同位置的性分配和繁殖成功一般存在差异,通常认为资源竞争、结构效应和交配环境是形成这种差异的主要原因。为了研究雄性和雌性繁殖资源在花序内不同位置间的最优分配问题,该文以青藏高原高寒草甸典型高山植物毛翠雀花为材料,通过比较花序内不同位置的花部特征和种子性状,对其花序内的性分配模式和雌性繁殖成功进行研究,并通过观察传粉者运动特点以及人工去花和补授花粉实验,探讨花序内资源竞争和交配环境对繁殖资源分配的影响。结果表明:(1)不同位置间的雄蕊数、雄蕊鲜重/雌蕊鲜重、花粉数及花粉胚珠比从花序基部到上部显著增加,而雌蕊鲜重和胚珠数逐渐减少,表现出上部花偏雄的性分配;上部花的结籽率显著低于基部花和中部花,不同位置间的发育种子数/果实和发育种子重/果实随着花位置的升高而显著降低,说明基部花具有更佳的雌性繁殖成效。(2)去花处理后,剩余果实的单个种子重/果实显著增加,但发育种子数/果实没有显著增加;而给上部花人工补授异花花粉后,位置间结籽率的差异消失,说明传粉限制而非资源竞争导致了花序内位置依赖的种子生产模式。(3)毛翠雀花雄性先熟的开花特征,以及传粉者苏氏熊蜂从花序基部到上部的定向访花行为,导致了花序内交配环境的变化。综上结果表明,毛翠雀花花序内的性分配和繁殖成功差异是对交配环境适应的结果,对其在高山环境中实现雌雄适合度最优化具有重要意义。     

Temporal patterns of seed set and decelerating fitness returns on female allocation in Zigadenus paniculatus (Liliaceae), an andromonoecious lily

I describe temporal patterns of seed production in the andromonoecious lily Zigadenus particulatus. Fruit set per flower and seed set per fruit declined through time within plants. Hand pollination experiments showed that this was not due to increasing pollen limitation. Nutrient supplementation had little effect on seed output, but leaf clipping reduced seed production, especially in late-blooming flowers, and removal of early-blooming flowers increased seed set by later flowers. Thus, the temporal pattern of seed output was due to declining availability of photosynthates. Plants with larger bulbs produced larger inflorescences, a greater proportion of hermaphrodite flowers, more fruits per hermaphrodite flower, and more seeds per fruit, but lost a greater fraction of their initial bulb mass as a consequence of fruiting. After controlling for the effects of bulb mass, plants with larger inflorescences produced a greater proportion of male flowers, and plants with more hermaphrodite flowers produced fewer fruits per hermaphrodite flower and fewer seeds per fruit. Thus, the female fitness gain curve was decelerating. The temporal decline in seed output provides a partial explanation for the parallel decline in allocation to pistils. However, a complete explanation for the pattern of gamete packaging requires an understanding of factors controlling male, as well as female, fitness.     

Extended flowering in a Mediterranean shrub: Seasonal variability in seed quality and quantity

Fluctuating conditions throughout the year and changes in floral display may promote shifts in pollinator activity and predator pressure, influencing female reproductive output, especially for extended flowering species under seasonal climates. In this regard, flowering and fruit production were tracked in 2 different years in 2 populations of Ononis tridentata in Central Spain. Total fruit production was estimated, and fruits were harvested to obtain primary fruit investment, pollination success, predation incidence, seed production, seed weight and germination rates. Ononis tridentata combined spring mass flowering with a steady long flowering period across the summer and fall. The fewer flowers that are produced in fall were successfully pollinated, and produced fruits that were subject to minimal predation pressure relative to spring fruits. Moreover, fall fruits contained a higher number of heavier seeds and showed higher germination rates than those of spring seeds. Fall reproductive output represent 10% of annual viable seeds and thus may act as an important complement to the main spring reproductive investment. Extended flowering could be interpreted as a “bet-hedging strategy” for enduring Mediterranean unpredictable and changing environmental conditions.